Thermostatic switch



Sept 14 1954 c. s. MERTLER 2,689,290

THERMosTA'rIc SWITCH Filed Oct. 30, 1951 l2 Sheets-Sheet l f3 .if I I 2f27 24,35 ffy 26 .iv

ai 11; j 1j-g' f? i555 BY 2 l@ f7@ '7 m/WZS.

Arron? Sept 14, 1954 c. s. MERTLER 2,689,290

THERMosTATIc swITcH Y Filed .001. 50. 1951 2 Sheets-Sheet 2 INVENTOR.CMRLe-.s .Me-Rz-LER Patented Sept. 14, 1954 t Ul\I'l 'l`E DV `STATESPATENT o OFFICE .f i 2,689,290

THERMosrATIc ,SWITCH Charles S. Mettler, MansiieldaOhio Applicationoctober so, 195"1 s`eria1 N0. 253,777

. l i This invention-'relates to electrical switchesand,`morparucu1ar1y,` to" thermostatic switches whicho-perate with asnap action at a predeterminedA temperature. An object `ofthe inventionis to provide improved thermostatic switches which operate with afsvnap`action within avery narrow temperature differential, thereby providingmoreV reliable control of an electrical circuit` or circuits, longercontact life, and reduced radio interference since fluttering or fryinglof the'contacts issubstantially eliminated, the switches being capableof carrying substantial currentloads` and rapidly responding to changesin temperature of thefenvironments in which they are mounted.

,Another object of theinvention is to provide an improved thermostaticswitch having a narrow temperature range or differential throughutilization of ra buckling or over-center spring to effect movement ofone'or more contacts of the switch, ythe said spring being anchored atonly one end thereof with the otherend free to snap and thereby effectcontact operationin response tothe force exerted on the spring by athermoresponsive member responding `to a predetermined change intemperature.

A further object of the invention is to provide an' improvedthermostatic'switoh as Vdefined in' r the preceding paragraph andwherein a means is provided cooperating. with the said buckling orover-center spring vto snap the latter'back to its initial position whenthe force exerted thereon by the thermoresponsive member is removed.v

vA stillfurther object of the Ainvention is lthe provision of animproved thermostatic switch as defined in either of the two precedingparagraphs and which is adapted 'to alternately `control two independentelectrical circuits in' response to a predetermined temperature change.l

Anjadditional object of the invention is to provide animprovedthermostatic switch 'employing an over-center or buckling springas one ofthe contacts thereof, the said spring being aotuatedby flexingoffthe centralv portion of a bimetallic member, whichmember has the endsthereof supported' for limited movement so that flexing ofthevbimetallic member in response to temperature changes is not hindered byits mounting. f i

`The,invention` also has as its object the pro-` vision of `ari/improvedthermostatic switch of the type denedabove and in which two or morevbimetallieinembers' are fioatingly supported adjacentftheover-center orbuckling spring for effecting operation of the' latter inresponselto apredetermined temperature change.

19 claims. (Cl, 29o- 138) Astill further object of the invention is toDrovidean improved` thermostatic switch as dened in `theprecedingparagraph and wherein the bimetallic membersare floatingly arranged insuperposed LAor stacked, motion additive,l re- .l lowing 4descriptionofthe present embodiment of theV invention and'certain modificationsthereof described with reference tol the accompanying drawingsy inwhich:

Fig'. l is a longitudinal sectional View through thefpresent preferredembodiment of a thermostatic switch incorporating the novel features ofthis invention with certain parts of the operating'mecham'sm being shownin elevation to more clearly illustratethe construction;

Fig. 2 is a bottom view of the switch illustrated inli'g. 1;`A

Figi 3 is a detached, elevational view of the present preferred form'ofover-center or buckling spring utilized in the switch illustrated inFigs. 1 and '2;`A v

Fig. 4 is a detached elevational view of theresilient contact-arm whichextends substantially parallel with the over-center spring in Fig. 1;

Fig.4 5 is a Vdetached elevational view of the member utilized toconnect the free ends of the over-center spring and resilient contactarm in the switch shown in Figs. 1 and 2i;

Fig. 6 is a longitudinal sectional view through a modied'from ofthermostatic switch embodying the invention with portions of theoperating mechanism shown in elevation to more clearly illustrate theconstruction;

Fig. 7 is a longitudinal sectional view through t a still different formof thermostatic switch embodying'the invention with portions of theoperatingV mechanism being shown in elevation to more clearly illustratethe construction;

Fig. 8 is a longitudinal sectional view through yet another form ofthermostaticswitch embodying the invention with portions of the op-55'11O0ki11g in thedirection indicated by the arrows;

and,

Fig. is a view similar to Fig. 8 but showing the positions of the partsof the switch` when the latter has been actuated in response toattainment of a predetermined temperature.

The thermostatic switches of this invention are of the snap action type,since the movable contact or contacts thereof move from one position tothe other relatively rapidly or with a snap action upon attainment of, apredetermined operating temperature. This rapid movement or snap actionprevents "fluttering, frying and similar diiculties which are present inthermostatic switches of the creep type. While switches of the snapaction type have many advantages, the principal ob- `iection thereto hasarisen from the fact that it is customary to employ relativelycomplicated mechanisms to effect the required snap action therebyincreasing the cost of the switches and multiplying the chances offailure of the switches in operation. In my copending applicationentitled Thermostatic Switch, S. N. 175,696, filed July 25,A 1950, Ihave disclosed and claimed improvements in thermostatic switches of thesnap acting type which enable the desired rapid movement of the contactsto be effected through the utilization of a single spring member, thusreducing the cost and at the same time providing a more reliableoperation. The switches of this invention are generally similar to thosedisclosed and claimed in the aforementioned copending application butdiffer therefrom in that the instant switches are particularly adaptedfor alternately controlling two independent electrical circuitsV and,i'n addition, have certain constructional features which differ from theswitches of the aforementioned application.

The spring element employed in the switches of this invention is forconvenience hereinafter referredv to as an over-center or buckling typespring. Such a spring may be formed in a variety ofM different mannersbut in the presently preferred embodiment the spring is of the typeillustrated in Fig. 3. As shown therein, the spring, generallydesignated I5, comprises an elongated`v strip of relatively' thin springmaterial' such as` tempered steel, brass, Phosphor bronze, or the like.This strip of material is longitudinally sl'otted or slit, asindicatedat` IBand I'I, parallel with the longitudinal edges of thestrip but with the ends of the slots or slits entirely enclosed withinthe edges ofthe spring. 'Ihere is thus provideda central portion A andouter portions B and C ofthe spring, which are all parts of the integralstrip. Thecentral portion A of the spring is elongated with respect tothe side portions B and C so that the spring tends to assume a curved"configuration, as viewed inside elevation, the direction of curvaturedepending upon whether the centrall portion A is disposed to one side orthe other of thev plane of the side portions B and C.

The central portion A of the spring I5maybe caused to snap throughcenter from one side of theplane of the; side portions B and C to theother side thereof by application of aforce in the nature of a thrust onthe said central portion, thereby causing the spring as a whole to curvein the opposite direction. Because the centralportion` A can never lieexactly in the plane of the side portions B1 and C but must alwaysbuckle. or snap through or beyond the center line or plane of suchportions, the spring issaidto bev of the over-center or buckling type.

In order to provide the` requisite difference in lengths between thecentral and sideA portions of the spring, the latter, in the form shownin Fig.

4 3, has had the side portions B and C reduced in length by crimping orcreasing them intermediate the ends of the spring as indicated at I8 andI9. This difference in length between the central portion A and the sideportions B and C of the spring may also be achieved by stretching thecentral portion with respect to the side portions. Moreover, while thespring I5 has been shown as constructed from one piece ofiv metal,I it.will?, be apparent tha-tit may, be formed 0f severalseparate piecesjoined together by welding or riveting. Springs of the forms mentionedas possible alternative constructions are illustrated and described inmyaforementioned copending application S. N.

, 175,696 to which reference may be had for the details thereof. Suchsprings may be interchangeablyused with respect to the spring I5 as mayother equivalent types and, therefore, it is to be expressly understoodthat the term overcenter or buckling spring as used in this descriptionand the appendedclaims is to` be construed" as generic of these variousAforms of spring and not limited toA a spring constructed'in any onespecific manner.

Referring now to Figs. 1V and 2;,the'switchshown therein is of' thethermostatic type adaptedto alternately control two independentelectrical circuits and includes an over-center or buckling spring ofthetype described'` above. The illustrated switch is ofthe enclosedtype-having'an oblong housing, generally designatedv 2m which may beformed from sheet metal by drawing, mayV be cast in one piece, ormay beassembled from several separate parts. In the form shown, the housingZIIis illustratedas being of one piececonstruction andfsubstantially U-shapedin longitudinal section, sov as` to provide a recess or cavitywithin which the operating portions ofthe switch are enclosed. Thehousing has outwardlyY extendiing ears or lugs ZI and'22 byv which thelswitch maybe applied to a surface the temperature ofV which is tolcontrol operation ofthe switch.

The top' of thehousing 20`ghas fourv terminal members 23, 24, 2'5` and'2% secured thereto in spaced relationship. In the form shown, theseterminal members each comprise substantiallyl right-angled bracketsl theopstanding legs of which are providedwith` tapped holesyl, 28', 29 and"30? for the receptionof; screws by means of which conductors may beconnected to the switch. The horizontal legs of thev terminal members:3f-28 are aperturedl and-are secured tothe housing, 20.by terminalposts or studs 3l, 32,33 andU 34; respectively, disposed' within thecavity ofthe housing and each having'a reduced `diameter portionextending through a cooperating opening in the housing Iand in thehorizontal portion ofV the. corresponding terminallug, the outer ends ofthev terminal posts being. peened ovenaswillbe apparent from Fig.. 1'.

posts 31:, $2-, stand 34 and vthefinneat"sidewall-oli` the housing.`insulationI is. shown asbeing. in

the: form ofisheet's orf platesf35'and 36`of` mica.;`

hard rubber, or other insulating material interposed as aforementioned,it being understood that the reducedy diameter portions yof the terminall posts are ofv less' diameter thanr the openings inr the housing 2U'through which they extendgjsee Fig. 1. In place; ofsheetsor plates ofinsulating, material, separate washers 4of insulating material' When, asthe illustratedA embodimentrthe case or. housing. lll is formed of.v

l. may be provided foreach terminal member and post. y

The terminal post 33 is preferably of lesser lengththan the terminalpost 32 with theinner end of the latter provided with a reduced diameterportion passing through an opening 31 at one end of vthe over-center orbuckling spring I5 and through ay corresponding opening in a relativelystiff resilient arm or member 38. A washer is preferably provided on thelower end of the post 32 and the latter is then peened over to firmlysecurefthe spring I5 and arm 38 in the relationship shown in Fig. 1. Asillustrated therein, the central portion A of the spring I 5 has anintegral raised surface 39 thereon provided by indenting the underside`of this portion of the spring as indicated at 40, see Fig. 13. Theouter end of the resilientarm 38 engages `the raised Yportion 39 of thespring either continuously or when the latter snaps through center andbears thereon with suf ficientforce so that the'central portion `Aof thespring -is-normally disposed below the' side portions B andeC when theparts are lpositionedV as shown in Fig. 1, and the temperature of theswitch has not been elevated sufliciently to actuate thethermoresponsivel member hereinafter described.

Consequently, theportion of the spring I5, op-` positefthe'post 32 isurged towards the terminal post 33 and this portion `of the spring* isprovided with a contact means or member 4I, which may be in the formof abutton of silver orother suit-'- able contact material spot welded -orotherwise secured to the spring I5. The construction is such that, withthe parts as shown in Fig. l, the contact 4I is in firm engagement withthe lower portion of the` terminal post 33 which may be providedwith asilveredfsurface or other'suitable material `providing a suitablecontact surface.

LThe lower portion of the terminal post 3| has a reduced diameter`portion extending through an opening in a resilient contact arm ormember 42 which -arm or member is rmlysecured to the post 3I by=peenin`g over the outer end `of the latter, a washer such as 43 beingpreferablyinterposed between the arm or member 42 and the peenedv outerendjof the terminal post 3l to insure proper support. The arm or member42 is adapted to flex or move in unison with the overcenter spring I5,this combined movement being effected by a connection between'thefree'ends oi" the-members in the form of a plate-like member or link 44which is formed of insulating material and is slotted as indicated atFig. 5 to rec'eive the louter ends ofthe spring I5 and memberv --Thelower Vsurface of the arm or member 42 is provided with means forming anelectrical contact which means is here illustrated as a button 45 'ofsilver or other suitable contact material spot welded or otherwisesecured to the'arm or member 42.V

The contact 45 is adapted to be moved to and from engagement with astationary contact 46 connected with the terminal post 34, the contact46 being here shown as a relatively rigid arm havinglacoating of `silverorv other suitable contact material on the upper surface thereof forengagementby the contact 45. Thel arm 46 is secured to! the post 34inany suitable manner, as, for example, by having a reduced diameterportion of the post passing through an opening in the arm or member 46with the outer end of this reduced diameter portion peened overas-showny in the drawings. e f' h`With the construction thusefardescribedfit will 6 bel apparent that the contact 4I normally inengagement with the terminal post or contact '33 while the contact 45 isspaced from the contact 46. fHowever, upon application of an upwardlydirectedforce or thrust upon the central portion Aof the over-centerspring I5, the latter will be caused to snap through center thusreversing the direction of its curvature so that the contact 4I movesfrom engagement with the terminal post or contact 33. Substantiallysimultaneously, the Contact 45-wi1l engage the contact 46 due to theinterconnection of the spring I5 with the resilient arm 42. vThis actionof the switch will result in ilexure of the arm 38, thus increasing theforce acting upon the raised portion 39 of the spring member I5 so thatwhen the upwardly directed force isreduced or removed the force exertedby' the member 38 automatically returns the parts tothe positions shownin Fig. 1.

In accordance with this invention the switch,

just described, is operated by a thermores-ponsive memberacting upon thecentral portion A of the' spring I5 to provide the upwardly directedforce when the temperature to which the switch is subjected equals orexceeds a predetermined value. For this purpose, the housing 26 has theend Wall slotted adjacent the ear or flange 22, slotted asy indicated at47, and an elongated, substantiall planar, bimetallic member or stri-p48 is positioned with one end freely passing through the slot 41v andwith the principal portion of the member extending interiorly of thehousing through sub-l stantially the length thereof. The inner endof thebimetallic member 48 is fioatingly supported within the housing by asupporting rod or mem-Vl ber 49, which extends freely throughv anopening in the inner end of the member 48. The lower end of the rod 44is provided with a iiange or collar` 5U on which the bimetallicfmember48 rests and, in order to reduce'friction between this collar 50 and thebimetallic member 48, the latter is preferably provided with spacedprojections such as 5I on either side of supporting member or rod 49,vthus elevating the main portion of the end of the member 48 slightlyabove the surface of the collar or flange 50.

The upper end of the rod or member 49 is in'- tegral with or connectedto an enlarged diameter provided with a radially projecting lugv 54 for'cooperating with an upstanding lug 55 on thev threaded bushing 53 tolimit the extent of adjustment of the shaft or member 52.

Intermediate its ends, the bimetallic member 48 has a recess or dimpleformed therein, which receives and supports the rounded lower end of aforce or thrust transmitting member 56. The member 56 is preferablyformed of insulating material and passes freely through an opening 42ain the arm 42 with its rounded upper end received in the recess ordimple 40 of the overcenter spring I5.

As mentioned heretofore, the housing 20 of the switch is preferably madeof metal and the ears 01 flanges 2| and -22 are placed upon and/orsecured--tothesurface whose temperature is to operate; the;v switch..Consequently/L theV4 thermo nosponsivemember; nam-elm. the:` bimetallic;strip.` ri'siin; ggodlthermai exchange relationship with: tl'leaaidi`surface; this being duebotlr tothe close,` pnoximity offy the:bimetallic" member with the surface as. welles the. fact4 that the.vends of the bimetallic member arerin rpositivemetal-to-metal: cantaorVwith the surface. through portions. of the housinggand of theswitchstructure: Thereore; the bimetallic member 48.` rapidly responds:tochanges. in temperature: ci?v the surface,y upon which` the switch ismounted, thereby flexing on bowing: intermediate: its ends.v In` theconstruction as showm, the bimetallic member is so disposed that. this.exing is. upwardly-1 asV viewed im the drawings and' isi unrestrained,since the cuter: ends of the. member may slide; upony the housing and.Acollar v50-1 respectively. Therefore, repeated iiexings on operations ofthe bimetallic. member 48-are always the same for the samepredetermined-temperature, there being noextraneousz stresses'introduced, as frequently happens when aI bimetallicmember' is rig-idlysecured to astationary` member.`

4The flexing of, thebimetallic member 46, in respense toan elevationv intemperature, exerts a` thrustupwardly upontthe spring, I5 through thelforcei.transmitting4 member 56fand, when a predetermined temperature hasbeen reached, this exing and the` resulting force are suflicient tocauscthe. spring I5. to snap through-center and move the contacts 4|-and 45, as has. beenl previ/:nisly` described, so thatthe contact 4=I nolonger eng-ages. the terminal or contact 33 and the contact 45 is now inengagement with the. contact 48.. WhenVv the. temperature of the surfaceon which the'iswitch -ismounted is loweredl below-the pi:enlctcrminedlvalue, the flexure of the bimetallic member 48ris reducedy sothatthethrust or force-,exerted through thej member B1-is corre.-spondingly lessened andtheresilient larm 38 `actsv upon the` spring l5to.- snap the latter back through. center to the position astshownv inFig. i.. The. temperature at which=the switchopera/-v tionnis eected maybe readily adjusted by turning the shaft or member 52 thus alteringthepositionof the. bi-rnetallic memberrelativeto the spring` I5 anld`thereby` altering` the amount of fiexure of the. bimetallic member48-necessary to eiiect switch. operation.

It i will. be evident`v that twoelectrical circuits maar be. alternatelycontrolled by a switch constructed as. just described Thus, one circuitmay. heconnected. toy the terminals 24 and 25fWhi1ean ,independent`circuit is. connected `tothe term-inals2`3. andy 2li1r Since theseterminal membersare insulated from` the housing and. from each other,the aforementioned circuits. can be com-` pirated.` only' when the`movable contacts such. as 41 45m-e in engagement withtheir cooperatinglstationaryy contacts 33 and'` 46, respectively. The construction of the.switch illustrated in Figs. 1`r andff2 is suchthatY the-circuit`connected to. the terminals, 241i and is normallyV completed andvtl.'lef circnity which. is connected to the terminals 23 and 25 isnormally `open with the first. circuit. lbeingfopcneci andyt'he second.circuit'closed upon thefattainment of aipredetermined temperature.Obviousiy, eitherY circuit: may be connected to either pair of terminalsand theinvention is inl nowise limited to the number orv nature ofycircuitswhich may` bev connected with the terminals.

While thesWitchshow-nin Figs', l-a-nd-zis illusA trated as` being of theclosed type, itwill be. readily apparent .that thesame. mode. of4operationv willbe effected. with arr4 open typeswitch.` In such: a.:construction, the support for the operating pori-i tions of: the'switch, would bev provided by;v a. substarrtla-lly li|1shapedy brackethaving open sidest rather than: the: closed sides which. are providsdt`butr the housing; 2m here illustrated; The opera.- tion of the switchisnot varied by this difference in themeunting; or housing. Moreover,although. thehousingA or mounting: 20. for the switch is l preferablymetallic to provide good heat ex.

change between the` bimetallic member4 and the surface on whichxtheswitch is mounted nevera theless,4 in some cases the housing. 2.0, orthe` equivalent supporting; bracket, may be Vformed of plastic. or otherinsulating lmaterial with the.` necessary heatexchange occurring throughthe. open bottomI ofthe housing..`

Fig. 6A shows amodiedform of switch embody-I ing the principles ofthis-invention andl employs ing` a buckling or over-center springsimilar to! that shown in Fig.. 14. embodiment' of the: switch is alsoshownasbeing'of the enclosedtype comprising a housing 51 identical withthe nous`4 ing 20ct Fig. 1.. In theinstant form,l the switch isAlikewise provided with terminal lugs 56, 59, and @which are secured; toterminal postsy SI1,` 62l andy 63i with interposed insulation such as.`64 and. B5, these parts-being identical. with corre.- sponding elements24, 25, 26, 32, 33, 34, 35v and 36in the form of the switchl shown invFigs. 1 and 2 and. hence need not, be again described detail. Similarly,the lower portion of the post 6i is-connected with one end. of anAover-center spring 61 andV the corresponding end'of aresilient arm 68,identical in construction and' function` with. the, spring. I5' and arm38. previously lde.- scribed. Also,.. the lower portion of the termi.-nal post. 63 is providedwith a contact arm 69 similar tothe contact arm46 of Fig. 1 andthe lower end ofl the terminal post. 62? isprovided asan electrical contact surfacelll,

In the form of the switch illustratedv in Fig. 6, there, are but. threeterminal members 56, 59,` 60. withv cooperating terminal posts and hencethe movable contact means or members controlled by the. spring` 61 areboth carried upon` the latter rather than one upon the4 over-centerlspring andthe other upon a connected `separate` arm. asin l. as will beseen in Fig. 6 the, outer or free end of the over-center spring 61 hasupper and lower contact members or buttons 'Hand 1.2'` provided thereonwith the formernormally engaged with the. contact portion or surface.160i the terminalI post 624 and with contact 12 normally spaced from butadapted to engage the contact 69 when the spring 6.1 snaps throughcenter.

Operation of the, spring` 61 and. hence of the movable, contacts 1l and.12 iseiected in response to attainment of a predetermined temperature bymeans of a bimetallic member. 13 having` one end supported` in a slot.or opening in` the housing 51- and the. other endy providedI with spacedprojections restingupon` a. collar or flange i the adjusting screw orpost 15. The; screw or post 15 is constructed in the samemanner andYoperates in they same wayfas the sup-A portingv andadjusting rod or postfor the thermo responsive member 48m* Fig. 1. The centralrpor-V tion ofvthebimetallic member 131v has a' recess or dimple in` the' uppersuriacethereof supporting the` lower end ofa force transmitting pin ormember-16, the upper endof whichis receivedv in a corresponding recessof the spring member 61= inthe same manner that the pin or member v56 issupported in the switch shownin Fig. l.

The operation of this embodiment of lthe invention is similar to thatpreviously described in that the attainment of a predeterminedtemperature `causes suicient force to be transmitted through the'memberor pin 16, as the result of flexing of the bimetallicfmember-13, tothereby snap 'the spring 61 throughcenter vso that the vcontact 1| ismoved from engagement with the contact surface or member and the contacti12 is` substantially simultaneously engaged with lthe contact 69,

Consequently, this switch may likewise be employed to control alternateopening `and closing of two separate circuits by con- 'nectingfone leadof each circuit to the terminal .1.1, .18 and 19 provided upon akhousing 80 in spacedk relationship and insulated` from each other byinsulating' members 8|, 82.1 in the same manner as in thepreviouslydescribed embodiments.` `The terminal Vmember. 11 is connectedat its innerfend with one end of an over-center spring. 83 'andthecorrespondingend `of aresilient arm 84, .identical with-the previouslydescribed springs and -cooperating arms.` 'I'he outer endn of the spring83i isprovided with upper and lower contact members 85 `and V86 formovement with the spring alternately from engagement withstationary-contact 81 and into engagement with a stationary contact 88,these contacts being provided Lupon the terminal-members 18 and 19,respectively; `as will now-be apparent. Inthis form ofvthe.invention,.however, the thermoresponsive member 89, While inthe'form offan elongated bim'etallic element, does not have: the

latter supported-in the same manner as in the two previously-describedembodiments.` Instead, one end ofthe vrbim'etallic member 89 is rigidlysecured to the side wall ei' the housing 80 as by rivets' 90,` or thellike, whioh pass through the `upturned-end or flange of the bimetallicelement.

Adjacent the inner or free endl of the bimetallic member 89 isarecessfor 'dimple in which is received `the lower endof a forcetransmitting member 9|', preferably formed of'insulating material, theupper end of which is received in the recess or dimple provided inthecentral portion of the over-center spring 83, this force transmittingmemberand its mountingibeing vsubstan- .tiallyithe samefas previouslydescribed.

A `means .for adjusting' the operation of the switch shown in Fig..v7 isprovided in the form of a threadedshaftonscrew 92 vhaving an outwardly,extendingdug93gcooperating with an upstanding lu'g 94 onathreadedbushing 95 secured `tothe housing andreceiving the threaded shaft 92'inthe same manner as the adjusting shafts or screws 52 and 15. In theinstant form of the invention, however, the lower end of the adjustingscrew or shaft 1,92 is provided with a reduced diameter extension 96which `may be a porcelain," ceramic, or like'insert having a roundedlower end and bearing'upon the upper surface of the bimetallic member 89intermediate the point of connection of the latter to the housing andthe force transmitting element 9 I.

The form of the invention illustratedinFi'g. 'Lmay be employed like theswitch Yillustrated in Fig, Gltoalternatelyv control opening and closingof two electrical circuits by connecting one lead of each circuit to theterminal member 11 and the other two leads respectively to terminalmembers 18 and 19. In the instant form of the invention a predeterminedtemperature change will cause flexing of the outer end of the bimetallicelement 89 upwardly as viewed in the drawings, thus acting upon thecentral portion of the overcenter spring 83 to snap the latter throughcenter and move` the contacts 85 and 86 from their illustrated positionsto the positions in which contact 39 engages contact-88 and contact 85is spaced from contact 81. When the temperature to which the switch issubjected drops below the predetermined value, the reduction in flexure'of ythe bimetallic member 89 will allow the arm screw or member 92 asit is retracted.

A still different embodiment of the invention is illustrated in Figs. 8through 10. As shown therein,.the `switch is of the single pole, doublethrow type and comprises terminal members 91, 98 and 99 secured to ahousing |00 by terminal posts |0|, |02 and |03, these parts being thesame as the terminals, terminal posts and housingvin Figs. 6 and 7.Also, as in the previous forms, the -instant embodiment is provided withinsulating members |04 and |05, which insulate theterminal members andvposts from the housing |00.` Similarly,-the terminal post |02 isprovided with astationary contact or contact surface |09 `and theterminal post |03 has a stationary lcontact |01connected therewith andeX- tending in spaced relationship to the contact |06. Also,- theterminal post |0| is connected at its lower endfwith one end of anover-center or buckling spring |09 immediately above which Vissupportedaresilient arm |0 which cooperates with 'the central portion of thespring to nory mally position the latter as shown in Fig. 8. The

outer end of the spring |09 is provided with upper and lower contactsand ||2 connected for movement with the spring and adapted to'alternately engage the stationary contacts |06, |01, respectively. Thespringresilient arm, and vcontacts are the same as in the previousembodiments, although the spring |09 is shown as having Ya multiplecrimp or bend in the side portions |09a,

and' |095 Yso as to provide a greater bow or arc of the centralk portion|090, thereby insuring greater movement of the contacts and ||2 when thespring is snapped through center. The operation ofthespring |09 and ofthe resilient arm I0 are, however, the same as has been previouslydescribed.

In the form of the invention illustrated in Figs. 8 through 10, thethermoresponsive means is in the form of one or more birnetallic stripsor plates, al plurality of such members being preferably employed1andarranged in vertically stacked order unsecured to each other or tothe other elements of the mechanism. As shown in the illustratedembodiment, two such bimetallic strips or members ||3 and ||4 areutilized which have `configurations substantially the same as but ofslightly smaller dimensions than the cavity or recess in the housing |00so as to freely flex therein without, however, being materiallydisplaced laterally or longitudinally. The bimetallic memu 'zafeeaecoubers'zor 'stripszare retained in vplace within the .housing 1| |10 byzabottomclosure :plate ror member v|`|5 extending vacross th'efbottom` ofthe housing andfwhich may" be .secured tothe .outwardly ex--tending-anges or ears such as thereofbi7 suitable means` suchras "spotwelding or the like. The `.bimetallicmember l||3 preferably has anYinitial curvature or `biasof relatively large radius `so that'the endsthereof -are raised slightly and .do not normallyrestupon the bottom orsupporting plate |15, .see Fig. 8. The lbimetallic member orstrippreferably vhas the central portion curvedslightly :so lasfto beelevatedabove :the `central portion of bimetallic strip v||3 and `the ends of.the member-H4 are reversely curved to ,provide arcuate surfaces "suchias lll'for engagement lwith the upper lsurface of themember ||3adjacent lthe ends of the latter.

,The central portionof `the-bimetallic element ror member `||f4 isprovided with a `means for .applying Vanupwa'rdly directed force Vorthrust upon the centraliportion' |09c of the spring |09. This thrustmember, designatedgenerally H8, is preferably -adjustable relative ItoAthe element `H4 yand is therefore disclosedas :a :post vor stud H9threaded fina :tapped central-'opening yof the Vbimetallic `element lIM.The upper .end of the stud 1H :is provided with a `reduced diameterextension, vpreferably ,in `the form of .a ceramic -or porcelain pinlikeinsert 4210, ythe upper end `of whichisireceivedin-a recess or'dimple inthe central portion |09c Tof the over-center fspring |09. Access 1to theilower-iportlon 4Lof the stud I r9 for -adjustingftheiforce transmittingymember may ,be yhad :through-:aligned openings in the lower .bimetallicmemberfll and in the bottom or cover y,plate =|r|5 .of theihousing.

The operationV ofthe-switch illustrated.l in Figs. Y.ii-10issimilarfin'vgeneral `prixrcipleszto those previouslyrdescribed, thebasic fdiilerence .being that the multiple .bimetallic .members .providefor `,greater -movement .per ndegree pf temperature .changeso "that Atheoverecenter spring `|09 can reflect greater distance'of 'movement of.the .con- `tacts ycarried thereby for a given .temperaturedifferential, with rthe result .that ygreater contact .separation can.be had thus `enabling the switch 'tto Ibe lnsedin installations .fwhererelatively `high vvoltages and/or currents (are iemployed.

Thepositions of theparts of the :switch when the latter is-at its coldernon-operated tempera- .ture :are illustrated "in ;Figs.81and"9 lfrom`which it will be seen'fthat the .contact 'illl .is=in.engage ment `withthe contact |||B and contact H2 is spaced from the contact JM,thecentral portion .of `the over-center .spring L09 being deflecteddownwardly under the forceof lthe-arm y|| 0 lwhich Ybears only upon thecentral `portion -|-|18c1of the spring. .Uponan .increase in.temperature of vthe environment in which -the switch ris placed, thebimetallic members ||3 and ||4 curve -in reverse directions, sincezthese `,members .are .disposed in motionadditive relationship. yWhenthe predetermined temperature `at .which .switch voperation is Adesiredhas `been attained, ythis deflection is sufficient tocause .the .centralVportion 09o of lthe spring lto .snap through center ythereby movingcontact .from engagement with contact ||J6 Aand. .bringing contact..|.|.2 into engagement with the contact |01., 'the .parts then being.substanftially asshown in .Fig. .10. When the tempera- `ture `of `theenvironment .in .which the switch is located drops below .theApredetermined value `efffecting toperationof theswitch, the curvature`oi. the bimetallic members IIB, .M4 will have `de- I2 creasedsulciently .so .that "the force of the arm ||0 willwcause -the centralportion `||l9c "of `the switch to again ysnap iback vthrough :center-returning the` contacts r1| |112 to their initialrpositions `as shownlin'fFig. 8. `The lterriperature `at which switch operation occurs maybereadilyladjusted by changingrthe position of the' force `transmittingmember I IB relative to the fbiinetallic member IM through the use of ascrew driver -or other suitable tool.

-It will now be apparenta switcho! thisioi'm .zmaylikewise be usedvtoalternately i' control two separate circuits I bywconnecting one wire of`each circuiti to the .terminal 91 and the `other ywires 1 of "thecircuits respectively tothe terminals 98 fand .99. It will `also`bef'evident thatmore'than-two .bimetallic elements such `as N and "H4vmay be` remployed in stacked relationship, if still greater Amovementper degree of temperaturechangeis desired, and i the .number 'of -su'chelements utilizedneed not beamultiple of two, ibut'may be an odd mumber.Moreover, .it .is 4not `necessary that vthe sidesoi the -fbimetallic.members having similar materials always-beplacedv adjacent each other,since in some-.instances it `is desirable that the members'be placedwith unlike materials ad jacent each lother.

The switch 'illustrated in Figs. Ii-10 `is of zthe sing-lepole,double-throw type. -It will be-fevident,

however, 'that `the ysame principles `may be lernbodied .in 1a `switchTof the single pole, single- `That f is to say., fit :is not necessaryfthat ythe .member HH ybe a stationary `contact 'where the switch isuto:control `but-a single circuit .by alternately :making and Vclosing'that (circuit.

V1n such .an installation, `the lcontact |-|2 rcoulel be omittedand.-thearm |01 could befsimplyin the 'iform `of an labutment ".to `limit'the movement lof -the outer y:end lci "the rover-center .spring M9.This extent `of movement :may -be made adjustable-by providing the saidabutment withianadjustablescrewlorlikefexpedient.

.Although feertainembodiments :of :the inventionfhave beenillustratedrand 'described'in -deltail,` it will Ibe evident that`modifications I may 'be [made in the `details oi the switches shown`and that the-'switches mayfbe utilized 'fior controlling a singrecircuitrather thantwo separate circuits. `For example, if the switches=be fused for Ycontrolling but a single circuit, they can loperate-either to open orclose'that-circuitiupon apredetermined rise intemperature by suitable connection .of the wires of the circuit to-theterminals.

`It willl-now-beevident thatthe inventionprovides thermostaticswitchesof the snap acting type rwhich Vare relatively simple in constructionyet reliable 'in operation and Vwhich require asmalleritemperaturediflerential for effecting operation than do-conventional "snap acting switches. `Furthermo`re,"the construction ofthe switches is-suchthatthe thermoresponsive members may be disposedclosely adjacent `the surface the heat of whichis to eilectswitchoperation so that 'the thermoresponsive members are affected by thermalconduction'through the metal portions of the housing and switch, as wellas by convection and radiation.

Other advantages and adaptations of the invention will be apparent tothose skilled in the art and hence `it `is to 'be understood that thedetailed drawings land ldescription are solely 'for the purpose ofillustrating certain practical embodiments of the invention and are notto lbe considered ias limitation thereon except as refaesaeco centerspring, meanssupporting said spring at 2 Aionly;one .end thereof,contact means connected with said spring adjacent the other end thereoffor movement therewith, a first stationary con- `tact normally engagedby said contact means, a

:second stationary contact electrically insulated and spaced from thesaid first stationary Contact and adapted to be engaged by the saidcontact y means when the latter is moved from engagement with the saidfirst stationary contact, thermo- Yresponsive means having a `portionadapted to move relative to said spring in response to changes intemperature, motion transmitting meansfextending between the saidportion and said spring at a location between the ends of the latter andexerting force on the spring when the said portion of thethermoresponsivemeans moves to-effeet snapping of said Vspring throughcenter Mtlnerebyrapidly moving said contact means from @engagementWith-said first stationary contact and into-engagement with said secondstationary con- 1 tact, means engaging said spring on the :opposite sideVthereof fromsaid motion transmitting means to effect resetting o f saidspring to its initial position, and separate terminal members connectedrespectively withsaid first and secondA contacts and with said contactmeans whereby the .saidrswitch is ladapted. for connection intwoelectrical circuits for alternate control thereof. f `2.A 4An electricalswitch comprisingan elongated ,over-center spring having ,acentralportion of greater lengthvthankthe sides thereof such that `thesaidv central portion is normally disposed on f oriefside or the otherof a plane containing said `sidejportions andis adapted `to move withasnap actionfrom one side to the other of the said I .ilaneuponapplication o f-foree thereto, means supporting said spring at only oneend thereof, contact `means connected with said` spring adjacent theother end thereof `f or movement therewith, .a first stationary contactnormally engaged yby the said contact means when the said central`portion of the spring is in one position, a second `stationary .contactelectrically,v insulated and lspacedqfrom the.V first stationary contactand `adapted to be engaged by the said contact means when the saidcentral portion of the spring is moved to the other `position thereof,aV thermoresponsive means having a portion adapted yto move relative rtosaid spring in response to changes yin. temperature, motiontransmittingv means-y extending b`etweenthe said portion of the-thermolresponsive means and the central portion of said spring'ata locationbetween` the V.ends -of the lattenand exerting `force on the `lattervwhen the said portion `of the thermoresponsive means moves to effectsnapping-of said spring through center thereby rapidly moving saidcontact means from engagement with said first contact and intoengagement with said second contact, and separate L terminal membersconnected `respectively withsaidfirst and second contactsandwith saidcontact means whereby the said switch is adapted for connection intwoelectrical circuits for alternate control thereof.' A

. v3`..A n. electrical switch comprising an overcenter spring, meanssupporting said spring at only one end thereof, contact means connectedwith said spring adjacent the other end thereof for movement therewith,a rsttatonary contact normally engaged by said contactimeans,

fro

fa second stationary contact'electricallyinsulated Uand spaced from thesaid rst stationary contact and'adapted to'be engaged by the saidcontact means when the latter `is .moved fromlengagement with the saidfirst l.stationary contact, an `elongated bimetallic member spaced from'said spring and having a 'portion free to flex in response totemperature changes, motion. transmitting means extending between thesaid portion of thebimetallic member and said aspring. at

Va location intermediate Vthe ends of the latter and adapted to exertlsufcient force on the latter v.when the bimetallic member exes apredetermined amount to thereby effect snapping of said `spring throughcenter thereby `rapidly'fmoving said contact means from engagementwithsaid :first stationary contact and into engagement with portionsandis adapted to. move with a snap action from one side to theother of saidplane upon application vof forcey thereto, means Vsupporting said springat only one end thereof, ycontact means connected with said spring:adjacent the other end thereof for movement therewith, afirst stationarycontact-.normally engaged bysaid con'- tact means,` a second stationarycontact electrically insulatedand spacedfrom the said first stationarycontact, and (adapted to be engaged fb'y the said contact means when thelatter.` is moved vfrom engagement withthe said rst stationary contact,an elongated bimetallic member spaced from saidspring `and having aportionfree toilex i n response to temperature changes, motiontrans--fmitting means extending between the said porftion ofthe bimetallicmemberand said spring'at alocation intermediate `the endsof th'e latterand adapted toexert a thrustof sufficient force Ton the latter when thevbimetallic member lexesy .a predetermined amountto therebyeffect"snapping of saidspringthrough center thereby rapid- 1y movingsaid contact means from engagement with saidY first stationary contactand'. into fengagement with said second stationary-contact, and means`engaging said spring on the sidefopposite the said motiontransmittingmeans. for exerting a .continuous vforce uponsaid spring'in.opposition to the thrust exerted thereon by 1ithe iiexure of thebimetallic member, `vvherebytlz said spring is automatically reset toits initial positionl after flexureA of said bimetallic member hassbeenreduced below the said predetermined amount;

5. Ani electrical` switch :comprising fan" overcenter spring; meansfsupporting said'spring `at only'one end thereof;l electricalcontact'members .on opposite*r sides of said,v spring" adja'cent the.other end thereof, a rststatonary contact normally engaged-by one ofthe; contactrmemberson said spring, a second stationary contactelectrif- 4ca llyinsulated and spacedwfrom thelsaidifirst stationarycontact and Vadapted to be engaged bythe other of said contact memberswhen. the .pret-mentioned contact member is moved `from engagement with:the said i'lrst stationary -contact, a lthermoresponsive means spacedfromsaid springs.. and. having a: `portion adapted toV move `message()Irelattve to said spring `in response to changes in temperature, motion`transmitting 4means extendbetween the said portion Aand said spring `ata :location between Athe 'ends of the latter and fexerltingforce onthelatter when the said portion iof the thermoresponsive lmeans moves toeffect snapping of said spring through center thereby -rapidly 4movingsaid first contact member from engagement with said lflrst stationary'contact ybringing said vsecond contact `member into =`engagement withsaid second stationary contact, resilientlmeansengagin'g said spring onthe oppo- -site side thereof from said vmotion transmitting 'uneans toeiect automatic return of said spring Aftolitsrinitial position, andseparate terminal memfbers connected respectively with said first andisecond contacts and with said contact -means whereby the said switch`is adapted lfor connection in two electrical `circuits for alternatecontrol thereof.

f6. Anelectrical switchcomprsing an over-cen- `ser spring, meanssupporting said spring at only ione end thereof, contact 'meansconnected ywith said spring adjacent the other end thereof for vmovementtherewith, a first stationary contact :normally engaged :by said contactmeans, a sectrind stationary `contact electrically insulated and-spacedfrom'the said first stationary contact and adapted to be engagedby the said contact means when 'the latter lis moved from engagementwith *tirevsaid first stationary contact, an elongated birmetallicmember spaced from said spring and having lits `ends supported forlimited movement and its --centralportion free to flex in response totemperature changes, motion transmitting means extending between thesaidcentral portion of the bimetallic member and said spring at a locationiintermediate the ends of the `latter and adapted Tto exert a thrust ofsufficient force on the latter `when the bimetallic vmember iiexes apredetermined'amount to'thereby effect snapping of said spring throughcenter thereby rapidly moving rsaid contact means `from engagement withsaid first s'tationarycontact and into engagement with said 'secondstationary contact, and separate terminal members connected respectivelywith said ,rst land ysecond contacts and with said contact means`whereby `the said switch is adapted for `commotion in two electricalcircuits for alternate control thereof.

7. An electricalswitch comprising an over-cen- Yter spring, meanssupporting said spring at only one end thereof, a contact member carriedby said 'springadjacent the other end thereof for movefment therewith, afirst stationary contact norfmally engaged by the said contact member, asecfond contact member connected for movement ywith lsaid spring andelectrically insulated from said `first contact member, a secondstationary Contact electrically insulated and spaced from the said rststationary contact yand adapted to be .engaged-'by the said secondcontact member when .the latter lis moved in response to movement ofsaid spring. a `thermoresponsive means having a zportionfadapted to moverelative lto said spring in .response to changes in temperature, motiontransmitting means extending between the said portion of thethermoresponsive means and said spring at a location between the ends ofthe ,latter and .exerting force on the latter when the :said 'portionmoves to eiect snapping of said spring through center thereby movingsaid `firstmentioned contact member from engagement .withfthe said first`stationary contact and bringling-the :said second contactmem'ber intoengagefspring adjacent the other "end thereof yfor LInovelmenttherewith, ia rst ystationary contact Inormally engaged by thefsaidcontact membenaasecond `contact, member, `means lmovably supporting saidsecond `contact memberadjacent tothe conftact ymember on said spring,vmeans yconnecting said vspring `and said second contact member mountingmeans `for movement itoge'the'r; la `second stationary contactelectrically insulated and spaced from the said first stationarylcortact member 'and adapted to be engaged by the said second contactmember when the 'latter lis imoved in response to movement of saidspring'a'thermo- `responsive means having a `por-tion adapted to moverelative to said spring in response ito changes in temperature, motiontransmitting means extending between the said portionof `thethermoresponsive means and said spring *at la location intermediate 'theends fof the latter 'and 'exerting force on ythe spring Awhenithe saidlportion lmoves `to effect snapping lof said spring 'through centerthereby Imoving said 'first-mentioned contact member from 'engagementwith the said first stationary contacts-andbring'ingithe said secondcontact member `into engagement with said second stationary contact, and'separate terminal members connected respectively with said first and`second contact ymembersand with said 'first and second stationarycontacts `whereby the said switch is adaptedfor connection in twoindependent electrical circuits for alternate `control thereof.

9. An electrical switch comprising-anover-center spring, meanslsupporting said spring atorily one end thereof, contact meansconnectedwith said spring adjacent the other end vtheredf vfor movementtherewith, va first Vstationary contact normally engaged by the saidcontact means, "a second stationary contact `electrically insulated andspaced from the said first stationary contact and adapted to be engagedby the said contact means when the latteriis moved fromengagement withthe said first stationary contact, an elongated lbimetallic memberspaced from said spring and having one end supportedto flex in responseto temperature changes, motion transmitting means extending between thesaid one `end portion of thebimetallic member land said uspring 'at alocation intermediate the ends of the vla-tter and adapted to exert Eathrust of sufficient force on'the latter when the bimetallicmemb'erfiexes a 'predetermined amount to effect "snapping of said springthrough center thereby rapidly moving said contact means from engagementwith said rst stationary contact and-into engagement with said secondstationary contact, resilient means engaging said spring on the opposite*si'de'thereo 'from said motion transmitting 'means to effect automaticreturn of said spring to its-initial position, and separate terminalmembers "connected respectively with said first and second contact andwith said contact means whereby 'the `said switch is adapted forconnection `in two independent electrical cir-cu'its for alternatecontrol thereof.

1117 re'. electoraat switch. comprising 9.a weecenteir spring, 'meanssupportingv saidi spring at only one end thereof, contact.y means.connected with saidl spring adjacent. the other' endthereof foi movementtherewith, a stationary.` contact normally engaged by the said contactmeans, a plurality of bimetallic members. supported in stackedrelationship and `having all"` portions thereof free for movement'responsa to= changes of temperature, motion. transmitting means; ex;-

tend'ing between one of saldi bimetallic: members and said spring at alocation between the; ends. or the latter for exerting force on thelatter when the bimetallic members hex toM effect snappingof saidaspring through centery thereby rapidly moving sad'i contact meansengagement; with said' stationary lcontact, and means. cooperating withsaid spring for resetting the latter to its initial position afterflexure oi' said bimetallic members has been reduced below the amountwhich` eiects snapping of said spring.

1l. An4 electrical switch comprising an overcenter spring, meanssupporting said spring yat only one end thereof, contact means connectedwith said spring adjacent the other end thereof for movement' therewith,a stationary contact normally engaged by the saidI contact,` means, aplurality of bimetallic members supported in motion additiverelationship, motion transmitting means extending between one of saidbimetallic members and said spring at a location'between the ends ofthel latter for exerting force on the latter when the bimetallic membersflex to eiect ,snappingof said spring; through center thereby rapidly'moving, said contact means from engagement with said stationary contact,and resilient means cooperating with said spring for automaticallyresetting the latter to its initial position after exure of saidbimetallic members has been reduced below the amount which effectssnapping of said spring.

12. An electrical switch comprising an elongated over-center springhaving a central portion of greater length than the sides thereof suchthat the said central portion is normally disposed on one side or theother of a plane containing said side portions and is adapted to movewith a snap action from one side to the other of the said plane uponapplication of force thereto, means supporting said spring at only oneend thereof, contact means connected'with said spring adjacent the otherend thereof for movement therewith, a stationary contact normallyengaged by said contact means, a plurality of bimetallicmemberssupported with all portions thereof free for movement in response tochanges of temperature and with the said members disposed in motionadditive relationship, motion transmitting means extending between oneof said bimetallic members and said spring at a location intermediatethe ends of the latter for exerting force on the latter when thebimetallic members flex to effect snapping of said spring through centerthereby rapidly moving said contact means from engagement with saidstationary contact, and means cooperating with said spring for resettingthe lattez` to its initial position after flexure of said bimetallicmembers has been reduced below the amount which eiiects snapping of saidspring.

13. An electrical switch comprising an overcenter spring, meanssupporting said spring at only one end thereof, contact means connectedwith said spring adjacent the other end thereof for movement therewith,la stationary contact normally engaged by said contact means, a pluralityof birnetallic'membersJ beneath said'spring 'in superposedf motionadditive relationship, moi- `salti contact means from engag/ement with.said stationary contact, and means cooperating with said spring torresettingA the. latter toits initial position after lexure of said.`bimetallic member has,A been reduced below the saidi predeterminedamount.

14. An electrical switchasz' defined in claim 13 andJ wherein the saidmeans for resettingsaid spring is a resilient member engaging theIspring on the side tl'lereoiiv opposite said bimetallic members andIacting in opposition thereto.

An electrical switch-comprising an overcenterl spring, means supportingsaid spring at only one endI` thereof', contact means connected withsaid spring adjacent the other end thereof for movement therewith,A arst stationary contact normally engaged by the contact means on sai-dspring, a secondstationary contact eleccally insulated and spaced fromthe first stationary contact, a plurality of bimetallic memberssupported in motion additive relationship and hav-ing all portionsthereof-l free tor movement response to. changes ot temperature,motion., transmitting means extending between one 0xff. said bimetallicmembers and said spring at a location intermediate the ends of thelatter for exerting force on the latter when. the. bimetallic membersflex to eect snapping of said spring through center thereby rapidlymoving said contact means from engagement with said rst stationarycontact and into engagement with said second stationary contact, andseparate terminal members connected respectively with said rst andsecond stationary contacts and with said contact means.

16. An electrical switch comprising a supporting means, a pair ofcontacts mounted on said supporting means in spaced relationship andelectrically insulated from each other, a movable contact means adaptedto alternately engage said spaced contacts, an over-center springsupporting said movable contact means at one end thereof with thecontact means normally in engagement with one of said spaced contacts,means at the other end of said spring mounting the latter uponv saidsupporting means, an elongated bimetallic member extending substantiallyparallel with said spring and spaced therefrom, means on said supportingmeans oatingly supporting said bimetallic member adjacent the endsthereof, and a thrust transmitting member intermediate the centralportion of said bimetallic member and said spring and adapted to causesaid spring to snap through center upon a predetermined flexure of saidbimetallic member in response to a predetermined temperature change,thereby moving said contact means into engagement with the other of saidspaced contacts.

17. An electrical switch as 'defined in claim 16 and wherein the meansfor supporting said bimetallic member includes an adjusting memberrotatably mounted on said supporting means and having a surface on whichone end of said bimetallic member rests.

18. An electrical switch comprising a supportsupporting' means in spacedrelationship and i9 electrically insulated from each other, a movablecontact means adapted to alternately engage said spaced contacts, anover-center spring supporting said movable contact means at one endthereof with the contact means normally in engagement with one of saidspaced contacts, means at the other end of said spring mounting thelatter upon said supporting means, an elongated bimetallic memberextending substantially parallel with said spring and spaced therefrom,means on said supporting means fioatingly supporting said bimetallicmember adjacent the ends thereof, a thrust transmitting memberintermediate the central portion of said bimetallic member and saidspring and adapted to cause said spring to snap through center upon apredetermined fiexure of said bimetallic member in re-` sponse to apredetermined temperature change, and resilient means engaging saidspring adjacent the central portion thereof and on the side thereofopposite the said thrust transmitting member and acting in a directionopposed to the thrust of the latter for automatically returning saidover-center spring and its contact means to their initial position afteriiexure of said bimetallic member has been reduced below the saidpredetermined amount.

19. An electrical switch comprising a supporting means, a pair ofcontacts'mounted on said supporting means in spaced relationship andtween said spaced contacts and normally engaged 20 with one of thelatter, an elongated bimetallic member extending substantially parallelwith said spring and spaced therefrom, means on said supporting meansrigidly mounting said bimetallic member adjacent one end thereof, amotion transmitting member adjacent the other end of said bimetallicmember and extending into engagement with said spring for causing thelatter to snap through center upon a predetermined fiexure of saidbimetallic member in response to a predetermined temperature change, andresilient means engaging said spring adjacent the central portionthereof and on the side thereof opposite the said motion transmittingmember and acting 1n a direction opposed to the latter for automaticallyreturning said over-center spring and its contact means to their initialposition after nexure of said bimetallic member has been reduced belowthe said predetermined amount.

References Cited in the i'ile of this patent UNITED STATES PATENTSNumber Name Date 1,733,085 Thomas Oct. 22, 1929 1,900,647 Hoopes Mar. 7,1933 2,004,772 Sonn June 11, 1935 2,060,836 Taxner Nov. 17, 19362,230,770 Van Almelo Feb. 7, 1941 2,295,456 Eaton Sept. 8, 19422,394,121 Ulanet Feb. 5, 1946 FOREIGN PATENTS Number Country Date655,549 Great Britain July 25, 1951 968,492 France Apr. 26, 1950

